The invention refers to an optical sensor to receive optical signals in a coating installation with an optical receiver for the reception of an optical signal, and such a coating installation. Also, the invention refers to a method for cleaning an optical sensor which is arranged in a coating installation.
Such optical sensors are used in coating installations, e.g. PVD-systems for the characterization of the condition or the position of the substrate, or the condition of a coating deposited on the substrate. According to the task requirements of the optical sensor, it is used in various steps along the process of a coating installation, and is exposed to various conditions of the surrounding environment. For instance for the characterization of the coating using an In-situ-measurement method, optical sensors are used within the coating chamber. The determination of the positions of the substrates using optical sensors, e.g. in a continuous method, serves mainly the accurate control of the course of the method in a coating installation. Both the characterization of the coating and the substrate, and the determination of the position of the substrate can take place in the coating chamber as well as in one of the process units of the coating installation arranged prior or subsequently, e.g. transfer chamber, buffer chamber, lock or other units for pre- and post-treatment of the substrate.
Within a coating chamber, mainly the coating parameters influence the functionality of an optical sensor directly. In particular through high temperatures or through coating material depositing on the sensor, the functionality of the optical sensor can be compromised. However in other units involved in the method of a coating installation, influences from adjacent units or from the substrate such as residual gas or coating materials, dust, high temperatures of the substrate or the chamber walls, temperature change or similar can also cause failures, malfunctions or at least distortion of measurement results of the optical sensor. Such effects shorten the intervals the optical sensors in coating installations is to be maintained considerably, and require more time and energy for maintenance or replacement within the vacuum area.
It is known to carry out the cleaning of an optical sensor using a gas flow the sensor is subjected to and completely surrounded by. Depending on the surrounding or the method conditions, the adaption can be done through, e.g. the configuration, dimensioning, location and alignment of the nozzle, through the choice of the gas, or through the pressure and temperature conditions of the gas which flows onto the optical receiver. Using a gas flow, accumulations on the substrate such as of dust or vapor-or particle-like coating material during the operating of a coating installation can be prevented by removing such dirt through a gas flow directed to the receiver before it deposits itself on it. Simultaneously, the temperature of the optical sensor can be specifically influenced by purposefully directing the flow of the gas.
The disadvantage of this kind of cleaning of the optical sensor is that an additional gas supply is needed, and further, an introduction of gas flows into the process atmosphere of the coating installation takes place which again leads to interferences with the stoichiometrical ratio during the gas phase of the coating installation and of the coating deposited on the substrate. For this reason, a stoichiometrically even deposition of a coating on the substrate can be interfered with. Another disadvantage derives from an introduction of the cooler gas flow into the process atmosphere through which the process temperature is interfered with, and for this reason, a temperature gradient is formed partly in the process atmosphere or on the substrate.
Also, optical fibers are generally suitable for the use in position measurement systems. The disadvantage here is also the contamination or rather the condensation through vapors at the end of the optical fibers which depending on the temperature of the process atmosphere quickly becomes unusable. Therefore, the actual functionality of the position measurement system is not ensured anymore.